Option to save archive without check recent and added preview default and button

Two small additions:
1. Added possibility to save Newsletter in archive even last saved is within one week. This is not default, but now is possible.
2. In Preview Newsletter form, added "Preview" button and now format type is pre-selected to match type determined in main Newsletter settings. Now is possible to preview with one click only, and to click the button again if administrator decide to change something and preview again.